It is the continuing goal of designers to increase the rate at which data can be transmitted over a packet switching system. Early packet switching systems comprised a single bus or coaxial cable which was used for all system functions. These systems were inherently slow since the cable was relatively long and had to be used for all system functions including, data transmission, arbitration and the exchange of control signals between ports.
The subsequently developed multibus packet switching systems provided increased data throughput. The reason for this was that the provision of the plurality of busses permitted the data transmission function, the arbitration function and control function to be accommodated over separate paths. This permitted the data bus to be used only for data transmission. Also, the provision of separate paths permitted arbitration and data transmission to take place concurrently. These improvements increased the system throughput. Systems of the multibus type are shown in U.S. Pat. No. 4,470,112 of Sept. 4, 1984, to J. O. Dimmick.
In the Dimmick type systems, data throughput is limited by the time required for the transmitting and receiving ports to perform their required system functions. Thus, for examle, a transmitting port requires a finite amount of time to read data out of the port's memory and apply it to the system data bus. Also, the receiving port requires a finite amount of time to receive the data sent to it over the bus and to enter this data into the port's memory device. The time required by the ports plus the but transit time is termed the system data transfer cycle.
The transit time required for the data to be transmitted over the bus is relatively short and is only a fraction of the time required by the transmitting and receiving ports to process the data. The system data throughput cannot be increased merely by increasing the system clock rate. If the ports are well designed and already operating at their capacity, an increase in the clock rate would only increase the error rate since the ports cannot process data any faster than they already are.
It is possible in certain specialized situations and systems that a port's data processing rate might be increased by the use of special high speed circuitry or devices. However, the use of such expedients is costly and, even then, can provide only a limited increase in data throughput.